CA2005848A1 - Centrifugal washer for paper pulp - Google Patents
Centrifugal washer for paper pulpInfo
- Publication number
- CA2005848A1 CA2005848A1 CA002005848A CA2005848A CA2005848A1 CA 2005848 A1 CA2005848 A1 CA 2005848A1 CA 002005848 A CA002005848 A CA 002005848A CA 2005848 A CA2005848 A CA 2005848A CA 2005848 A1 CA2005848 A1 CA 2005848A1
- Authority
- CA
- Canada
- Prior art keywords
- cylinder
- pulp
- recited
- interior
- arcuate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
- D21C9/06—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents in filters ; Washing of concentrated pulp, e.g. pulp mats, on filtering surfaces
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/18—De-watering; Elimination of cooking or pulp-treating liquors from the pulp
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
- Centrifugal Separators (AREA)
- Filtration Of Liquid (AREA)
Abstract
ABSTRACT
A method and apparatus provide for the effective centrifugal washing and/or thickening of paper pulp, using a perforated cylinder. A stock head box, located within the cylinder, applies a thin sheet of pulp on the interior the cylinder, at a high rate (e.g. about 20 meters per second), at a first arcuate position. The cylinder is rotated at high speed (e.g. 100 rpm, to provide an acceleration on the order of about 10 gs), whereby centrifugal force causes liquid in the pulp to move radially outwardly through the openings in the screen cylinder. The pulp is withdrawn from the interior of the cylinder by a vacuum roll or the like at a second arcuate position less than 360° from the first position. The withdrawn pulp is moved by a screw conveyor or the like away from the cylinder in a dimension generally parallel to the axis of rotation, and the withdrawn liquid passes through channels in a drum surrounding the perforated cylinder, and is engaged by an impeller, and flows to a volute for removal. Wash water may be added by a wash water head box within the cylinder between the first and second arcuate positions. A drive roll operatively engages the exterior of the cylinder for effecting rotation.
A method and apparatus provide for the effective centrifugal washing and/or thickening of paper pulp, using a perforated cylinder. A stock head box, located within the cylinder, applies a thin sheet of pulp on the interior the cylinder, at a high rate (e.g. about 20 meters per second), at a first arcuate position. The cylinder is rotated at high speed (e.g. 100 rpm, to provide an acceleration on the order of about 10 gs), whereby centrifugal force causes liquid in the pulp to move radially outwardly through the openings in the screen cylinder. The pulp is withdrawn from the interior of the cylinder by a vacuum roll or the like at a second arcuate position less than 360° from the first position. The withdrawn pulp is moved by a screw conveyor or the like away from the cylinder in a dimension generally parallel to the axis of rotation, and the withdrawn liquid passes through channels in a drum surrounding the perforated cylinder, and is engaged by an impeller, and flows to a volute for removal. Wash water may be added by a wash water head box within the cylinder between the first and second arcuate positions. A drive roll operatively engages the exterior of the cylinder for effecting rotation.
Description
~. Z005i8~L8 CE~TRIFUGAL WAS~ER FOR PAXER PULP
( BACKGROUND AND 5U~MAR~ OF T~R: INVENTION
Washers and thickeners are relatively expensive components of conventional pulp mills. Conventional thickeners and washers usually comprise a cylindrical drum to which a vacuum is applied over the forming and washing zones. The rate of application of the pulp as a sheet to the rotating vacuum drum exterior surface is typically 510w, on the order of about 1 meter per second for conventional pressure washers. The drum also rotates relatively slowly, on the order of about 4 rpm. Therefore, the amount o;E pulp treated per-screen area is relatively small. Since the cost of conventional thickeners/washers is strongly dependent upon their size, such devices typically end up being e~pensive components of the mills.
It has been recognized that the thinner the layer of pulp through which the water must travel, the faster the thickening and washing operation3 can be accomplished, and the smaller the thickening/washing machine may be. However the art has not been able to make practical use of this known phy~ical phenomena.
One way that use of the thin sheet advantages - can be achieved is by utilizing centriugal force to cause the filtrate to move through the pulp. In U.S. patent 3,289,843, an apparatu~ is described having ~everal different embodiments for centrifugal washing/filtering. However such centrifuges have not proven particularly effective in the pulp and 2~1~)584~
,. .
paper field.
( According to the present invention, a method and apparatus are provided that take advantage of centrifugal force to cause thin sheets of pulp to be formed on a screen, and also provide the motive force for moving the filtrate through the pulp.
Utilizing the invention, it is possible that washers having about a 10 times smaller screen area compared to conventional vacuum ~rum washers are possible, thickening and washing can be obtained without any rubbin~ seals to confine a vacuum or the like, there is no necessity for external devices such as droplegs, vacuum pumps, or fans, to provide the motive force for water to move through the pulp.
According to one aspect of the present invention, an advantageous pulp thickener/washer is provided which comprises the following elements:
(a) A perforaked cylinder hav:ing an interior and an exterior. (b) Means for applying pulp in a thin sheet on the interior of the cylinder at a first arcuate position thereof. (c) Means for rotating th~ cylinder about an axis of rotation so that liguid in the sheet is caused to move radially outwardly through the cylinder as a result of c~ntrifugal force, so that the pulp is thickened.
(d) Means for withdrawing the pulp from the interior of the cylinder at a second arcuate position, le~s than 360~ from the first position. (e) Means for moving the withdrawn liqui~ and treated pulp away from the thickener/washsr for sub~equent treatment, use, or dispo~al. And, (f) means for applying wash water ko the pulp at the interior of the cylinder at a third arcuate position between the irst and (, second positions.
( The ~leans (b~ preferably comprises a stock head box similar to that utilized to form sheets of paper or pulp. The velocity of pulp from the head box, which is provide~ by line pressure, is preferably at least about 10 meters per second, and typically at least about 20 meters per second, to approximately match the speed of the rotating cylinder. The means () also comprises a wash watar head box. The means (d) preferably comprises a vacuum roll, although an air doctor or steam doctor alternatively may be utilized. The means (e) can be selected from a wide variety of chutes, conveyors, or the like, but preferably comprises a screw conveyor extending in a dimen~ion generally parallel to the axis of rotation of the screen cylinder. The means (e) for filtrate removal preferably comprises means defining channels in a drum surrounding the screen, an impeller, and a volute, with a cut-off shoe for the impeller at an arcuate section generally between the first and second arcuate positions, to facilitate pulp removal at that point. The means (c) preferably comprise~ a drive roller which operatively engages the exterior of the cylinder to rotate it about a generally horizontal axi~, and the cylinder may be a cylindrical perforated plate, or a cylindrical wire cloth.
According to another aspect of the present invention, a method o~ acting on paper pulp to thickan and/or wa~h it utilizing centrifugal ~orce is provided. The effective method according to the inv~ntion comprises the steps of substantially se~uentially: (a) Applying pulp in a thin sheet on 5~
an interior of the cylinder at a first arcuate ( position. (b) Rotating the cylinder about its axis to cause liquid in the pulp to move radially outwardly, under the influence of centrifugal force, through the cylinder, to be discharged. (c~
Withdrawing the sheet from the cylinder at a second arcuate position less than 360~ from the first position. (d) Passing the pulp to a further treatment or use stage. And, (e) adding wash water to the interior of the sheet betwe~n the first and second arcuate positions. Step (a) is practiced at a rate oE at least about 10 meters per second (e.g.
about 20 meters per second), and step (b) is practiced at a rate of at least about 2~ rpm (e.g.
about 100 rpm). Paper pulps entering at a wide variety of consistencies may be treated, and will typically have a consistency of about 8-12% during and/or after treatment.
It is the primary object of the present invention to provide for the efective washing and/or thickening o paper pu:Lp or like suspensions, utilizing centrifugal force as the main motive force for filtrate movement. Practicing the invention it is possible to reduce the screen area/daily ton of pulp processed, thereby significantly decreasing washer costs, while at the same time providing effective treatment. These and other object~ o the invention will become clear from an inspection of the detailed de~cription of the invention and from the appended claims.
2~(~5~
BRI~F DESRIPTION OE T~ DRA~IN~S
( EIGURE 1 is a side schematic view o an exemplary pulp thickener/washer according to the invention;
FIGURE 2 is an end view, partly in cross-section and partly in elevation, taken along lines 2-2 of FIGURE 1, of the device of FIGURE l;
and FIGURE 3 is a diagrammatic illustration of the pulp in liguid movements in the device of FIGURES 1 and 2.
DE~AIr.~ DESCRIPTION OE TEE DR~WINGS
An exemplary washer/thickener according to the present invention is shown generally by reference numeral 10 in FIGURES 1 and 2. Major components of the device 10 comprise: a perforated cylinder l~
having an interior surface and an exterior surface;
mean~ -- such as ~tock head bo~ 14 -- for applying pulp 15 in a thin sheet on the interior of the cylinder 12; means, such as the drive roll 16 and idl~r 18, for rotating the cylinder about an axis 20; means, such as vacuum roll 22, for withdrawing the pulp from the. interior of the cylinder; and means, ~uch as the 3crew conveyor 24 for the pulp, and the stationary volute 26 and associated components ~or the filtrate, for withdrawing the liguid and treated pulp away from the thickener and washer 10 for subsequent treatment, use, or ! disposal. Also, there preferably is provided a means -- such as wash water head box 28 -- for applying wash water to the pulp.
The stock is applied to the interior of the cylinder 12 by the stock head box 14 or the like at a first arcuate position 30. The head box 14 is similar to that utili~ed to form sheets of paper pulp. The high velocity is provided by the line pressure to the head box 14, and the velocity typically is at least about 10 meters per second, e.g. about 20 meters per second. The velocity of ~ the pulp is adjusted to approxima~ely match the : speed of the rotating cylinder 12. This compares with a velocity of one meter per second in conventional pressure washers.
.. The vacuum roll 22, or like pulp withdrawal : means such as an air doctor or st~am doctor, i~ withdraws the pulp from the interior surface of the - 20 cylinder 12 at a second arcuate position 31, which is less than 360 from the first position 30. That ` i8, there i~ a positive arcuate angle 32 between the positions 30, 31. In the exemplary embodiment ~; illustrated in FIGURE 2, the an~le 32 is about 40, : 25 meaning that the arcuate spacin~ of th~ pulp application position 30 and the pulp withdrawal position 31 in the direction of rotation 33 i5 about 320. Wash water i8 applied by the wa~h water head ; box ~80 Head box 28 is located in an arcuate po~ition 34 between the ~irst and second positions 30, 31, and preferably closer to the head box 14 than the vacuum roll 2~. It should be positioned ( where the heet 15 has had sufficient li~uid ,~
., ~
centriugally withdrawn to have good integrity, but ( before air begins to be drawn into the sheet. For example in the exemplary embodiment illustrated in FIGURE 2, the arcuate spacing between the head boxes 14, 28 is on the order of 80.
The cylinder 12 has perforations therein through which filtrate flows, while the pulp remains in contact therewi-th. The cylinder 12 may be made in a wide variety of conventional forms. For in~tance it may be provided as a perforated plate, or it may be A wire cloth, both of which are presently commonly used in vacuum wa~hers. Wire cloth may be particularly advantageous becauss it lets less fibers through, however it may pose a problem because the pulp is applied to the interior of the cylinder. Therefore when a wire cloth is utilized as the cylinder 12, it may be desirable to use expandable hoops to hold the wire taut against the interior of drum 38 with a turn buckle at the - splits of each hoop to expand the hoops tightly into place.
The mean~ for removing the filtrate which pas~e~ radially outwardly through the thin sheet of pulp 15 preferably includes a drum 38, and acce~sory components. The drum 38 is exterior of the cylinder 12, and provides ~upport for it so that the cylinder itself may be very thin. The drum 38 has means defining radial, axial, and/or circumferential channels 40 there~n, which lead filtrate from both ends of the drum toward opening~ along the equator of the drum 38. To magnify the differentiaL
pres~ure further, the iltrate pas~e~ through a clo~ed impeller 42 of a centrifugal pump at the :
Z~
vvlute 26. The filtrate is then cvllected in the ( volute 26, which surrounds the impeller section.
The volute 26 does not need to rub the impeller to prevent water from leaking out at that point since centriugal force holcls the water on the outside of the volute. Any plash which might be aimed at the opening would likewi~e b~ thrown back into the volute by the rotation of the impeller. Filtrate is discharged from the volute at one or more points 43, 44, to external piping, so that the filtrate is removed for ~ubsequent treatment, use, or disposal.
In order to help release the pulp sheet 15 for discharge at the second arcuata position 31, preferably a shoe 46 is provided extending an arcuate distance slightly greater than the angle 32, between the first and second positions 30, 31. The shoe covers the impeller at that area, which cuts of the differantial pressure and facilitates release of the 3hset 15 to the perforated surface of - 20 the vacuum roll 22. Also a back flow of air or water may be applied through the shoe 46 to compen~ate or leakage around it, i necessary.
The drive roll 16 is driven by a conven4ional :~ motor to achieve a high rate o drum speed, e.g.
preferably at least about 25 rpm, for axample about 100 rpm, ~o that the centrifugal force will be high, the ~heet 15 will be thin, and the filtrate will move ~uickly through the sheet for complete treatment in the relatively ~mall arcuate extent of about 320 between the first and second po~itions 30, 31. The drive roll 16 operatively engages the .exterior o the cylinder 12 through the drum 38.
Other acce~ory component3 may al80 be .~
utilized. For example a conventional wire cleaner ( 50 may be provided on the interior of the cylinder 12 acting on the insid~ surface of the cylinder 12 within the angular position 32, and a warning roll 51 may also be provided in that arcuate area. Also, a pulp containing trough 52 may be provided around the screw conveyor 24, the s_rew conveyor 24 being rotatable about an a~is that is generally parallel ; to the axis 20 o rotation of the screen cylinder 12, which axis 20 preferably is horizontal. Instead of the screw conveyor 24, however, other types of conveyors, an inclined chute, or a sluice may ~e utilized.
The method according to the invention comprises a method of acting on paper pulp, or like suspensions, which may have a wide variety of consistencie~, for example on the order of about 1/4-14% (the range over which head boxes have been known to operate or are expected to operate in the future). The method comprises the steps of substantially sequentially: Applying pulp in a thîn ; ~heet 15 on the interior of the cylinder 12 at the first arcuate position 30. Rotating the cylinder 12 about axis 20, at high speed (e.g. to achieve a drum speed o~ at least about 25 rpm, for example 1~0 rpm) -- so a to achieve acceleration on the order of about 10 gs. -- to cause the li~uid in the pulp to move radially outwardly through the cylinder 1 under the influence of centrifugal force to be discharged. (This high rotational speed, and acceleration, inherently assists in en~uring that the ~heet 15 is thin.) Withdrawing the sheet of pulp 15 from the cylinder 12 at the ~econd arcuate (~
position 31 less than 360 (e.g. on the order of ! about 320) from the first position 30, utilizing the vacuum roll 22, cut-off shoe 46, and the like.
Pa6sing the pulp, utilizing screw conveyor 24 and trough 52, or the like, to a further treatment or use stage; and preferably adding wash water to the interior of the ~heet at the arcuate position 34, utilizing wash water head box 28 or the like. The wash water addition arcuate position 34 is disposed at a point where the sheet 15 has reached a consistency firm enough to avoid being disrupted, but be~ore much air becomes entrained therein.
In the practice of the method according to the inventio~, air that i~ entrained either in the filtrate or the pulp will also tend to be centrifuged out of the system. Further, the filtrate is discharged at such a velocity that it has a considerable head, and it can be transported in the conduits 43, 44 to wherever it is needed without further pumping or further tankage-. The pulp sheet 15 may be applied at a high rate by the head box 14, e.g. at at least about 10 meters per second (for example 20 meters per second~, compared to about one meter per ~econd in the prior art~ The ~peed is adju~ted to approximately match that of the rotary cylinder. Thus effective treatment of pulp utilizing e~uipment having a minimal screen area per ton of pulp proce~sed, is provided.
According to the invention a method and apparatus have been described which have a number of advantages over the conventional system~. Because a very thin sheet 15 of pulp is provided due to the centrifugal force that exist~ because of the high ~, ~ )S8~8 rate of 6peed o the cylinder, washers having about ( 10 times a smaller screen area than i8 conventional may be provided. Diffarential pressure is enhanced because the filtrate has a finite depth as it is drained from the pulp at the point (the volute 26 of the equator of the drum 38) where the liquid discharges from the drum. No rubbing seals are necessary to confine the vacuum or the pressure differ~ntial, and pressure differential is not produced b~ any external device such as a dropleg, vacuum pump, or fan. No additional devices are nece~sary to pump the removed filtrate to additional use or ~torage areas, and air inherently is removed from the system. While the advantageou~ method and ; 15 apparatus according to the invention have been shown ~; in what is presently conceived to be the most -!- practical and preferred embodiment thereof, it will be apparent to those of ordinary skill in the art that many modifications may b~e made thereof within ~ 20 the scope of the invention, which æcope is to be accorded the broadest interpretation~of the appended claims so a~ to encompass all e~uivalent ~tructures and methods.
( BACKGROUND AND 5U~MAR~ OF T~R: INVENTION
Washers and thickeners are relatively expensive components of conventional pulp mills. Conventional thickeners and washers usually comprise a cylindrical drum to which a vacuum is applied over the forming and washing zones. The rate of application of the pulp as a sheet to the rotating vacuum drum exterior surface is typically 510w, on the order of about 1 meter per second for conventional pressure washers. The drum also rotates relatively slowly, on the order of about 4 rpm. Therefore, the amount o;E pulp treated per-screen area is relatively small. Since the cost of conventional thickeners/washers is strongly dependent upon their size, such devices typically end up being e~pensive components of the mills.
It has been recognized that the thinner the layer of pulp through which the water must travel, the faster the thickening and washing operation3 can be accomplished, and the smaller the thickening/washing machine may be. However the art has not been able to make practical use of this known phy~ical phenomena.
One way that use of the thin sheet advantages - can be achieved is by utilizing centriugal force to cause the filtrate to move through the pulp. In U.S. patent 3,289,843, an apparatu~ is described having ~everal different embodiments for centrifugal washing/filtering. However such centrifuges have not proven particularly effective in the pulp and 2~1~)584~
,. .
paper field.
( According to the present invention, a method and apparatus are provided that take advantage of centrifugal force to cause thin sheets of pulp to be formed on a screen, and also provide the motive force for moving the filtrate through the pulp.
Utilizing the invention, it is possible that washers having about a 10 times smaller screen area compared to conventional vacuum ~rum washers are possible, thickening and washing can be obtained without any rubbin~ seals to confine a vacuum or the like, there is no necessity for external devices such as droplegs, vacuum pumps, or fans, to provide the motive force for water to move through the pulp.
According to one aspect of the present invention, an advantageous pulp thickener/washer is provided which comprises the following elements:
(a) A perforaked cylinder hav:ing an interior and an exterior. (b) Means for applying pulp in a thin sheet on the interior of the cylinder at a first arcuate position thereof. (c) Means for rotating th~ cylinder about an axis of rotation so that liguid in the sheet is caused to move radially outwardly through the cylinder as a result of c~ntrifugal force, so that the pulp is thickened.
(d) Means for withdrawing the pulp from the interior of the cylinder at a second arcuate position, le~s than 360~ from the first position. (e) Means for moving the withdrawn liqui~ and treated pulp away from the thickener/washsr for sub~equent treatment, use, or dispo~al. And, (f) means for applying wash water ko the pulp at the interior of the cylinder at a third arcuate position between the irst and (, second positions.
( The ~leans (b~ preferably comprises a stock head box similar to that utilized to form sheets of paper or pulp. The velocity of pulp from the head box, which is provide~ by line pressure, is preferably at least about 10 meters per second, and typically at least about 20 meters per second, to approximately match the speed of the rotating cylinder. The means () also comprises a wash watar head box. The means (d) preferably comprises a vacuum roll, although an air doctor or steam doctor alternatively may be utilized. The means (e) can be selected from a wide variety of chutes, conveyors, or the like, but preferably comprises a screw conveyor extending in a dimen~ion generally parallel to the axis of rotation of the screen cylinder. The means (e) for filtrate removal preferably comprises means defining channels in a drum surrounding the screen, an impeller, and a volute, with a cut-off shoe for the impeller at an arcuate section generally between the first and second arcuate positions, to facilitate pulp removal at that point. The means (c) preferably comprise~ a drive roller which operatively engages the exterior of the cylinder to rotate it about a generally horizontal axi~, and the cylinder may be a cylindrical perforated plate, or a cylindrical wire cloth.
According to another aspect of the present invention, a method o~ acting on paper pulp to thickan and/or wa~h it utilizing centrifugal ~orce is provided. The effective method according to the inv~ntion comprises the steps of substantially se~uentially: (a) Applying pulp in a thin sheet on 5~
an interior of the cylinder at a first arcuate ( position. (b) Rotating the cylinder about its axis to cause liquid in the pulp to move radially outwardly, under the influence of centrifugal force, through the cylinder, to be discharged. (c~
Withdrawing the sheet from the cylinder at a second arcuate position less than 360~ from the first position. (d) Passing the pulp to a further treatment or use stage. And, (e) adding wash water to the interior of the sheet betwe~n the first and second arcuate positions. Step (a) is practiced at a rate oE at least about 10 meters per second (e.g.
about 20 meters per second), and step (b) is practiced at a rate of at least about 2~ rpm (e.g.
about 100 rpm). Paper pulps entering at a wide variety of consistencies may be treated, and will typically have a consistency of about 8-12% during and/or after treatment.
It is the primary object of the present invention to provide for the efective washing and/or thickening o paper pu:Lp or like suspensions, utilizing centrifugal force as the main motive force for filtrate movement. Practicing the invention it is possible to reduce the screen area/daily ton of pulp processed, thereby significantly decreasing washer costs, while at the same time providing effective treatment. These and other object~ o the invention will become clear from an inspection of the detailed de~cription of the invention and from the appended claims.
2~(~5~
BRI~F DESRIPTION OE T~ DRA~IN~S
( EIGURE 1 is a side schematic view o an exemplary pulp thickener/washer according to the invention;
FIGURE 2 is an end view, partly in cross-section and partly in elevation, taken along lines 2-2 of FIGURE 1, of the device of FIGURE l;
and FIGURE 3 is a diagrammatic illustration of the pulp in liguid movements in the device of FIGURES 1 and 2.
DE~AIr.~ DESCRIPTION OE TEE DR~WINGS
An exemplary washer/thickener according to the present invention is shown generally by reference numeral 10 in FIGURES 1 and 2. Major components of the device 10 comprise: a perforated cylinder l~
having an interior surface and an exterior surface;
mean~ -- such as ~tock head bo~ 14 -- for applying pulp 15 in a thin sheet on the interior of the cylinder 12; means, such as the drive roll 16 and idl~r 18, for rotating the cylinder about an axis 20; means, such as vacuum roll 22, for withdrawing the pulp from the. interior of the cylinder; and means, ~uch as the 3crew conveyor 24 for the pulp, and the stationary volute 26 and associated components ~or the filtrate, for withdrawing the liguid and treated pulp away from the thickener and washer 10 for subsequent treatment, use, or ! disposal. Also, there preferably is provided a means -- such as wash water head box 28 -- for applying wash water to the pulp.
The stock is applied to the interior of the cylinder 12 by the stock head box 14 or the like at a first arcuate position 30. The head box 14 is similar to that utili~ed to form sheets of paper pulp. The high velocity is provided by the line pressure to the head box 14, and the velocity typically is at least about 10 meters per second, e.g. about 20 meters per second. The velocity of ~ the pulp is adjusted to approxima~ely match the : speed of the rotating cylinder 12. This compares with a velocity of one meter per second in conventional pressure washers.
.. The vacuum roll 22, or like pulp withdrawal : means such as an air doctor or st~am doctor, i~ withdraws the pulp from the interior surface of the - 20 cylinder 12 at a second arcuate position 31, which is less than 360 from the first position 30. That ` i8, there i~ a positive arcuate angle 32 between the positions 30, 31. In the exemplary embodiment ~; illustrated in FIGURE 2, the an~le 32 is about 40, : 25 meaning that the arcuate spacin~ of th~ pulp application position 30 and the pulp withdrawal position 31 in the direction of rotation 33 i5 about 320. Wash water i8 applied by the wa~h water head ; box ~80 Head box 28 is located in an arcuate po~ition 34 between the ~irst and second positions 30, 31, and preferably closer to the head box 14 than the vacuum roll 2~. It should be positioned ( where the heet 15 has had sufficient li~uid ,~
., ~
centriugally withdrawn to have good integrity, but ( before air begins to be drawn into the sheet. For example in the exemplary embodiment illustrated in FIGURE 2, the arcuate spacing between the head boxes 14, 28 is on the order of 80.
The cylinder 12 has perforations therein through which filtrate flows, while the pulp remains in contact therewi-th. The cylinder 12 may be made in a wide variety of conventional forms. For in~tance it may be provided as a perforated plate, or it may be A wire cloth, both of which are presently commonly used in vacuum wa~hers. Wire cloth may be particularly advantageous becauss it lets less fibers through, however it may pose a problem because the pulp is applied to the interior of the cylinder. Therefore when a wire cloth is utilized as the cylinder 12, it may be desirable to use expandable hoops to hold the wire taut against the interior of drum 38 with a turn buckle at the - splits of each hoop to expand the hoops tightly into place.
The mean~ for removing the filtrate which pas~e~ radially outwardly through the thin sheet of pulp 15 preferably includes a drum 38, and acce~sory components. The drum 38 is exterior of the cylinder 12, and provides ~upport for it so that the cylinder itself may be very thin. The drum 38 has means defining radial, axial, and/or circumferential channels 40 there~n, which lead filtrate from both ends of the drum toward opening~ along the equator of the drum 38. To magnify the differentiaL
pres~ure further, the iltrate pas~e~ through a clo~ed impeller 42 of a centrifugal pump at the :
Z~
vvlute 26. The filtrate is then cvllected in the ( volute 26, which surrounds the impeller section.
The volute 26 does not need to rub the impeller to prevent water from leaking out at that point since centriugal force holcls the water on the outside of the volute. Any plash which might be aimed at the opening would likewi~e b~ thrown back into the volute by the rotation of the impeller. Filtrate is discharged from the volute at one or more points 43, 44, to external piping, so that the filtrate is removed for ~ubsequent treatment, use, or disposal.
In order to help release the pulp sheet 15 for discharge at the second arcuata position 31, preferably a shoe 46 is provided extending an arcuate distance slightly greater than the angle 32, between the first and second positions 30, 31. The shoe covers the impeller at that area, which cuts of the differantial pressure and facilitates release of the 3hset 15 to the perforated surface of - 20 the vacuum roll 22. Also a back flow of air or water may be applied through the shoe 46 to compen~ate or leakage around it, i necessary.
The drive roll 16 is driven by a conven4ional :~ motor to achieve a high rate o drum speed, e.g.
preferably at least about 25 rpm, for axample about 100 rpm, ~o that the centrifugal force will be high, the ~heet 15 will be thin, and the filtrate will move ~uickly through the sheet for complete treatment in the relatively ~mall arcuate extent of about 320 between the first and second po~itions 30, 31. The drive roll 16 operatively engages the .exterior o the cylinder 12 through the drum 38.
Other acce~ory component3 may al80 be .~
utilized. For example a conventional wire cleaner ( 50 may be provided on the interior of the cylinder 12 acting on the insid~ surface of the cylinder 12 within the angular position 32, and a warning roll 51 may also be provided in that arcuate area. Also, a pulp containing trough 52 may be provided around the screw conveyor 24, the s_rew conveyor 24 being rotatable about an a~is that is generally parallel ; to the axis 20 o rotation of the screen cylinder 12, which axis 20 preferably is horizontal. Instead of the screw conveyor 24, however, other types of conveyors, an inclined chute, or a sluice may ~e utilized.
The method according to the invention comprises a method of acting on paper pulp, or like suspensions, which may have a wide variety of consistencie~, for example on the order of about 1/4-14% (the range over which head boxes have been known to operate or are expected to operate in the future). The method comprises the steps of substantially sequentially: Applying pulp in a thîn ; ~heet 15 on the interior of the cylinder 12 at the first arcuate position 30. Rotating the cylinder 12 about axis 20, at high speed (e.g. to achieve a drum speed o~ at least about 25 rpm, for example 1~0 rpm) -- so a to achieve acceleration on the order of about 10 gs. -- to cause the li~uid in the pulp to move radially outwardly through the cylinder 1 under the influence of centrifugal force to be discharged. (This high rotational speed, and acceleration, inherently assists in en~uring that the ~heet 15 is thin.) Withdrawing the sheet of pulp 15 from the cylinder 12 at the ~econd arcuate (~
position 31 less than 360 (e.g. on the order of ! about 320) from the first position 30, utilizing the vacuum roll 22, cut-off shoe 46, and the like.
Pa6sing the pulp, utilizing screw conveyor 24 and trough 52, or the like, to a further treatment or use stage; and preferably adding wash water to the interior of the ~heet at the arcuate position 34, utilizing wash water head box 28 or the like. The wash water addition arcuate position 34 is disposed at a point where the sheet 15 has reached a consistency firm enough to avoid being disrupted, but be~ore much air becomes entrained therein.
In the practice of the method according to the inventio~, air that i~ entrained either in the filtrate or the pulp will also tend to be centrifuged out of the system. Further, the filtrate is discharged at such a velocity that it has a considerable head, and it can be transported in the conduits 43, 44 to wherever it is needed without further pumping or further tankage-. The pulp sheet 15 may be applied at a high rate by the head box 14, e.g. at at least about 10 meters per second (for example 20 meters per second~, compared to about one meter per ~econd in the prior art~ The ~peed is adju~ted to approximately match that of the rotary cylinder. Thus effective treatment of pulp utilizing e~uipment having a minimal screen area per ton of pulp proce~sed, is provided.
According to the invention a method and apparatus have been described which have a number of advantages over the conventional system~. Because a very thin sheet 15 of pulp is provided due to the centrifugal force that exist~ because of the high ~, ~ )S8~8 rate of 6peed o the cylinder, washers having about ( 10 times a smaller screen area than i8 conventional may be provided. Diffarential pressure is enhanced because the filtrate has a finite depth as it is drained from the pulp at the point (the volute 26 of the equator of the drum 38) where the liquid discharges from the drum. No rubbing seals are necessary to confine the vacuum or the pressure differ~ntial, and pressure differential is not produced b~ any external device such as a dropleg, vacuum pump, or fan. No additional devices are nece~sary to pump the removed filtrate to additional use or ~torage areas, and air inherently is removed from the system. While the advantageou~ method and ; 15 apparatus according to the invention have been shown ~; in what is presently conceived to be the most -!- practical and preferred embodiment thereof, it will be apparent to those of ordinary skill in the art that many modifications may b~e made thereof within ~ 20 the scope of the invention, which æcope is to be accorded the broadest interpretation~of the appended claims so a~ to encompass all e~uivalent ~tructures and methods.
Claims (20)
1. A pulp thickener/washer comprising:
(a) a perforated cylinder having an interior and an exterior;
(b) means for applying pulp in a thin sheet on the interior of said cylinder at a first arcuate position thereof;
(c) means for rotating said cylinder about an axis of rotation so that liquid in the sheet is caused to move radially outwardly through the cylinder as a result of centrifugal force, so that the pulp is thickened;
(d) means for withdrawing the pulp from the interior of the cylinder at a second arcuate position, less than 360° from said first position; and (e) means for moving the withdrawn liquid and treated pulp away from the thickener/washer for subsequent treatment, use, or disposal.
(a) a perforated cylinder having an interior and an exterior;
(b) means for applying pulp in a thin sheet on the interior of said cylinder at a first arcuate position thereof;
(c) means for rotating said cylinder about an axis of rotation so that liquid in the sheet is caused to move radially outwardly through the cylinder as a result of centrifugal force, so that the pulp is thickened;
(d) means for withdrawing the pulp from the interior of the cylinder at a second arcuate position, less than 360° from said first position; and (e) means for moving the withdrawn liquid and treated pulp away from the thickener/washer for subsequent treatment, use, or disposal.
2. A device as recited in claim 1 further comprising (f) means for applying wash water to the pulp at the interior of the cylinder at a third arcuate position between said first and second positions.
3. A device as recited in claim 2 wherein said means (b) comprises a stock head box, and said means (f) comprises a wash water head box.
4. A device as recited in claim 3 wherein said means (d) comprises a vacuum roll.
5. A device as recited in claim 4 wherein said means (e) comprises, for the pulp, a screw conveyor rotatable about an axis generally parallel to the axis of rotation of said cylinder, in a trough.
6. A device as recited in claim 4 wherein said means (e), for the withdrawn liquid, comprises a drum surrounding said cylinder, means defining channels in said drum extending to an impeller, and a volute surrounding said impeller.
7. A device as recited in claim 6 wherein said means (d) further comprises a cut-off shoe extending over an arcuate section of said impeller an arcuate length generally corresponding to the shortest arcuate section between said first and second positions.
8. A device as recited in claim 1 wherein said cylinder comprises a cylindrical perforated plate.
9. A device as recited in claim 1 wherein said cylinder comprises a cylindrical wire cloth.
10. A device as recited in claim 1 wherein said means (c) comprises a drive roll operatively engaging the exterior of said cylinder to rotate it about a generally horizontal axis.
11. A method of acting on pulp to thicken and/or wash it utilizing centrifugal force, and utilizing a perforated cylinder having an interior and an exterior and rotatable about an axis, said method comprising the steps of substantially sequentially:
(a) applying pulp in a thin sheet on an interior surface of the cylinder at a first arcuate position;
(b) rotating the cylinder about its axis to cause liquid in the pulp to move radially outwardly, under the influence of centrifugal force, through the cylinder, to be discharged;
(c) withdrawing the sheet from the cylinder at a second arcuate position less than 360° from the first position in the direction of rotation; and (d) passing the pulp to a further treatment or use stage.
(a) applying pulp in a thin sheet on an interior surface of the cylinder at a first arcuate position;
(b) rotating the cylinder about its axis to cause liquid in the pulp to move radially outwardly, under the influence of centrifugal force, through the cylinder, to be discharged;
(c) withdrawing the sheet from the cylinder at a second arcuate position less than 360° from the first position in the direction of rotation; and (d) passing the pulp to a further treatment or use stage.
12. A method as recited in claim 11 wherein step (a) is practiced at a rate approximating the rotational speed of the rotating cylinder.
13. A method as recited in claim 12 wherein step (a) is practiced at a rate of about 20 meters per second.
14. A method as recited in claim 12 wherein step (b) is practiced to provide a drum speed of at least about 25 rpm.
15. A method as recited in claim 14 wherein step (b) is practiced to achieve an acceleration of about 10 gs.
16. A method as recited in claim 14 comprising the further step (e) of adding wash water to the interior of the sheet between the first and second arcuate positions.
17. A method as recited in claim 11 wherein step (c) is practiced by applying a vacuum to the interior of the sheet at the second arcuate position.
18. A method as recited in claim 11 wherein step (b) is practiced to achieve an acceleration of about 10 gs.
19. A method as recited in claim 11 comprising the further step (e) of adding wash water to the interior of the sheet between the first and second arcuate positions.
20. Pulp treating apparatus comprising:
a perforated cylinder having an interior and an exterior;
a stock head box located within the cylinder adjacent the cylinder interior;
a wash water head box located within said cylinder adjacent the cylinder interior, at an arcuate position spaced from said stock head box;
a vacuum roll located within said cylinder adjacent the cylinder interior at an arcuate position between said stock head box and wash water head box;
pulp conveying means adjacent said vacuum roll and operatively associated therewith;
a volute surrounding said screen at a portion thereof; and means disposed exteriorly of the cylinder and operatively engaging the cylinder for effecting rotation thereof about an axsis.
a perforated cylinder having an interior and an exterior;
a stock head box located within the cylinder adjacent the cylinder interior;
a wash water head box located within said cylinder adjacent the cylinder interior, at an arcuate position spaced from said stock head box;
a vacuum roll located within said cylinder adjacent the cylinder interior at an arcuate position between said stock head box and wash water head box;
pulp conveying means adjacent said vacuum roll and operatively associated therewith;
a volute surrounding said screen at a portion thereof; and means disposed exteriorly of the cylinder and operatively engaging the cylinder for effecting rotation thereof about an axsis.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US435,035 | 1989-11-13 | ||
| US07/435,035 US5013460A (en) | 1989-11-13 | 1989-11-13 | Centrifugal washer for paper pulp with means to feed pulp as a thin sheet |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2005848A1 true CA2005848A1 (en) | 1991-05-13 |
Family
ID=23726698
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002005848A Abandoned CA2005848A1 (en) | 1989-11-13 | 1989-12-18 | Centrifugal washer for paper pulp |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5013460A (en) |
| EP (1) | EP0428004A1 (en) |
| JP (1) | JPH03167383A (en) |
| BR (1) | BR9005718A (en) |
| CA (1) | CA2005848A1 (en) |
| FI (1) | FI905416A0 (en) |
| NO (1) | NO904900L (en) |
| ZA (1) | ZA908117B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE469232C (en) * | 1992-04-08 | 1997-08-18 | Kvaerner Pulping Tech | Method and apparatus for washing cellulose pulp |
| EP0778908B1 (en) * | 1994-08-31 | 2001-05-09 | The Hoffman Group Ltd. | Thin mat washing of cellulosic pulp |
| US6228215B1 (en) | 1998-04-06 | 2001-05-08 | Hoffman Enviornmental Systems, Inc. | Method for countercurrent treatment of slurries |
| BR9909540A (en) | 1998-04-08 | 2000-12-12 | Thermo Black Clawson Inc | Apparatus for processing paper pulp, sieve disk refiner and method of processing a pulp suspension |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1531482A (en) * | 1922-06-19 | 1925-03-31 | Anton J Haug | Paper-making machine |
| US1717604A (en) * | 1927-10-04 | 1929-06-18 | Anton J Haug | Process and machine for thickening pulp |
| US3114309A (en) * | 1962-01-24 | 1963-12-17 | Ingersoll Rand Canada | Centrifugal thickener for paper pulp |
| US3289843A (en) * | 1964-03-19 | 1966-12-06 | Dorr Oliver Inc | Apparatus for centrifugal screening |
| US3642139A (en) * | 1968-08-12 | 1972-02-15 | Peter C Wilson | Apparatus for centrifugally removing liquid from a mixture |
| GB1294980A (en) * | 1970-05-11 | 1972-11-01 | ||
| AT333682B (en) * | 1973-05-09 | 1976-12-10 | Westfalia Separator Ag | METHOD FOR OBTAINING STARCH FROM THE CELLULAR TISSUE OF HEDGE FRUITS, E.G. POTATOES |
| SU897299A1 (en) * | 1977-04-25 | 1982-01-15 | Туркменский государственный научно-исследовательский и проектный институт нефтяной промышленности | Centrifugal machine |
| US4186097A (en) * | 1978-10-30 | 1980-01-29 | Reclamet, Inc. | Shiftable bottom wall for separator bowl and wear shoe therefor |
| US4698919A (en) * | 1986-04-08 | 1987-10-13 | Beloit Corp. | Apparatus for assisting the transfer of a web to a drying section |
| US4827741A (en) * | 1988-03-21 | 1989-05-09 | Ingersoll-Rand Company | Pulp washer discharging a pulp slurry at a controlled consistency |
-
1989
- 1989-11-13 US US07/435,035 patent/US5013460A/en not_active Expired - Fee Related
- 1989-12-18 CA CA002005848A patent/CA2005848A1/en not_active Abandoned
-
1990
- 1990-10-11 ZA ZA908117A patent/ZA908117B/en unknown
- 1990-10-30 EP EP90120777A patent/EP0428004A1/en not_active Withdrawn
- 1990-11-01 FI FI905416A patent/FI905416A0/en not_active IP Right Cessation
- 1990-11-07 JP JP2302328A patent/JPH03167383A/en active Pending
- 1990-11-12 NO NO90904900A patent/NO904900L/en unknown
- 1990-11-12 BR BR909005718A patent/BR9005718A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| NO904900D0 (en) | 1990-11-12 |
| BR9005718A (en) | 1991-09-17 |
| JPH03167383A (en) | 1991-07-19 |
| NO904900L (en) | 1991-05-14 |
| US5013460A (en) | 1991-05-07 |
| FI905416A0 (en) | 1990-11-01 |
| EP0428004A1 (en) | 1991-05-22 |
| ZA908117B (en) | 1991-07-31 |
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